and also depends what kind of steel you are talking about. martensite, sphereodite, pearlite, etc. steel production is different for every grade of steel, the quenching could get very difficult for some. also, good steal nowadays is not just iron and carbon anymore, for example 304 grade stainless steel (the most common stainless steel) is composed of carbon, manganese, silicon, potasium, sulphur, chromium, molybdenum, nickle, nitrogen, and iron. even within 304 grade, there are basic 304, 304H and 304L. with totally different tensile strength, yield strength, hardness and elongation. not every steel mill in a country is going to be producing a single kind of steel, they probably specialize in one kind depends on market. so to say that all steel is 6 billion yrs old is false. china can meet her depands for certain grades of steel, but can't for others. that's y china exports and import steel. export the excess steel she produce and import the steel she needs.
eg. tensile strength for 304 is 205MPa, 304L is 170MPa <---- huge difference